The internal quantum efficiency of the near-band-edge (NBE) excitonic photoluminescence (PL) in ZnO epilayers was significantly improved by eliminating point defects, as well as by the use of ZnO high-temperature-annealed self-buffer layer (HITAB) on a substrate as epitaxial templates. Negatively charged Zn vacancy concentration was greatly reduced by high-temperature growth, and slower postgrowth cooling (annealing) under minimum oxygen pressure further reduced the gross concentration of positively and negatively charged and neutral point defects, according to the suppression of nonequilibrium defect quenching. The nonradiative PL lifetime at room temperature was increased by decreasing the gross concentration of point defects, as well as by decreasing the concentration of . Accordingly, certain point defect complexes incorporated with ( complexes) are assigned to the dominant nonradiative recombination centers. As a result of the elimination of point defects, a record long at was demonstrated. Because the radiative lifetime is in principle constant in bulk and epitaxial ZnO, the increase in gave rise to the increase in . Rich structures originating from exciton-polaritons and excited states of excitons were eventually observed in the low-temperature PL spectrum of the improved ZnO epilayer on HITAB, of which of the NBE emission was 6.3% at .
Improvements in quantum efficiency of excitonic emissions in ZnO epilayers by the elimination of point defects
Author to whom correspondence should be addressed; also at NICP, ERATO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan and Photodynamics Research Center, RIKEN (Institute of Physical and Chemical Research), Aoba, Sendai 980-0868, Japan; electronic mail: optoelec@bk.tsukuba.ac.jp
Also at NICP, ERATO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan.
Also at Nanomaterials Laboratory, National Institute for Materials Science, Tsukuba 305-0003, Japan.
Also at Combinatorial Materials Exploration and Technology (COMET), Tsukuba 305-0044, Japan.
S. F. Chichibu, T. Onuma, M. Kubota, A. Uedono, T. Sota, A. Tsukazaki, A. Ohtomo, M. Kawasaki; Improvements in quantum efficiency of excitonic emissions in ZnO epilayers by the elimination of point defects. J. Appl. Phys. 1 May 2006; 99 (9): 093505. https://doi.org/10.1063/1.2193162
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